Single side band (SSB) mixers are used in a wide range of electronic equipment, particularly in radio and other high frequency equipment where there is a need to mix frequencies in an additive or subtractive manner, or to compare phases of different signals. Some of the typical circuits employing SSB mixers include frequency synthesizers, quadrature demodulators and up-converters.
One example of a prior art SSB mixer is taught by U.S. Pat. No. 6,496,545 entitled SINGLE SIDE-BAND MIXER which achieves a high level of sideband rejection, but does so with significant circuit complexity and also requires fabrication in a BiCMOS integrated circuit process in order to achieve sufficient matching of components to control parameters such as phase angle error. The circuit complexity and BiCMOS process requirements both add undesirable cost to this SSB mixer.
The bandwidth limitations of prior art SSB mixers are demonstrated in a frequency synthesizer that provides a wide frequency range along with improved noise performance. U.S. Pat. No. 6,977,556 entitled RATIONAL FREQUENCY SYNTHESIZERS discloses the use of multiple SSB mixers for a range of frequency ratios based on the output frequency and the reference frequency. While this invention enables performance across a wide frequency range, the use of multiple SSB mixers, ratio dividers and associated control circuitry is a complex and potentially expensive approach to providing a wide frequency range with low noise.